Certain forms of diarrhea, namely those caused by the production of enterotoxins by certain bacteria are often difficult to treat and can be life threatening. The use of normal antidiarrheal agents which merely are absorbents, such as kaolin, or agents that reduce intestinal muscle activity have little or no effect on this enterotoxin-caused diarrhea.
Cholera is an acute infection in man involving the entire small bowel, characterized by a debilitating diarrhea. Enterotoxigenic Escherichia coli are a major cause of diarrhea in neonatal food-producing animals and "travelers diarrhea" in man.
These enteric bacteria release enterotoxins that interact with the epithelium of the small intestine, the effects of which result in water and electrolyte transport reversing from absorption to secretion. V. cholerae enterotoxin and Escherichia coli LT enterotoxin stimulate adenylate cyclase causing increased formation of cAMP which, through a cascade of reactions, inhibits active absorption and stimulates active secretion of water and electrolytes (sodium, chloride, bicarbonate). In contrast to these two enterotoxins, Escherichia coli ST enterotoxin stimulates guanylate cyclase, increasing cGMP levels, which causes diarrhea primarily by inhibiting active absorption of water and electrolytes.